25,26,27,28-Tetrakis(3-bromobenzyloxy)calix[4]arene

In the title compound, C56H44Br4O4, the calix[4]arene unit displays the 1,2-alternate conformation with crystallograpically imposed inversion symmetry. The four phenoxy rings of the calix[4]arene unit are twisted about the mean plane defined by the four methylene C atoms bridging the benzene rings, with dihedral angles of 46.73 (6) and 66.11 (5)°. The dihedral angle between adjacent phenoxy rings is 74.75 (7)°. The two pendant bromophenyl rings on the same side of the calix[4]arene unit are nearly perpendicular to each other, with a dihedral angle of 72.85 (10)° due to an intramolecular C—H⋯π interaction. In the crystal, a Br⋯Br contact of 3.6350 (5) Å, an intermolecular C—H⋯Br hydrogen bond and an intermolecular C—H⋯π interaction are observed.

In the title compound, C 56 H 44 Br 4 O 4 , the calix[4]arene unit displays the 1,2-alternate conformation with crystallograpically imposed inversion symmetry. The four phenoxy rings of the calix [4]arene unit are twisted about the mean plane defined by the four methylene C atoms bridging the benzene rings, with dihedral angles of 46.73 (6) and 66.11 (5) . The dihedral angle between adjacent phenoxy rings is 74.75 (7) . The two pendant bromophenyl rings on the same side of the calix[4]arene unit are nearly perpendicular to each other, with a dihedral angle of 72.85 (10) due to an intramolecular C-HÁ Á Á interaction. In the crystal, a BrÁ Á ÁBr contact of 3.6350 (5) Å , an intermolecular C-HÁ Á ÁBr hydrogen bond and an intermolecular C-HÁ Á Á interaction are observed.
Cg1 and Cg2 are the centroids of the C23-C28 and C7-C12 rings, respectively.  (Gutsche, 2008;Ikeda & Shinkai, 1997) and crystal engineering (Dalgrano et al., 2007) because they can be easily modified by selective reactions involving the upper and/or the lower rim of the molecule (Asfari et al., 2001;Mandolini & Ungaro, 2000). Calix[4]arenes can adopt several conformations, of which the 1,2-alternate conformation is much less commonly found. For that reason, the title compound, adopting the 1,2-alternate conformation, was prepared for use as a starting material for the preparation of ligands for construction of metallo-supramolecular architectures via appropriate chemical modification at the bromine positions.
In the crystal structure of the title compound, as shown in Fig. 1, the calix[4] unit adopts an 1,2-alternate conformation, located on a crystallographic inversion centre. Therefore the asymmetric unit consists of one half-molecule. The four phenoxy rings of the calix[4]arene unit are twisted about the mean plane defined by the four methylene C atoms (C13, C14, C13 i and C14 i ) bridging the benzene rings, with dihedral angles of 46.73 (6)° for the C1-C6 ring and 66.11 (5)° for the C7-C12 ring (symmetry code: (i) -x, -y + 2, -z + 1). The adjacent phenoxy rings make a dihedral angle of 74.75 (7)°. The two pendant bromophenyl rings on the same side of the calix[4]arene unit are nearly perpendicular to each other, with a dihedral angle of 72.85 (10)° due to the intramolecular C-H···π interaction; Cg1 is the centroid of the C23-C28 ring, H17··· Cg1 2.74 Å and C17-H17···Cg1 174.5 ° (Table 1, Fig. 1).
In the crystal structure, as shown in Fig. 2, a Br···Br contact of 3.6350 (5) Å, an intermolecular C-H···Br hydrogen bond and intermolecular C-H···π interaction are observed (Table 1). These intermolecular interactions may contribute to the stabilization of the crystal packing.

Experimental
To a refluxing suspension of calix[4]arene (2.00 g, 4.71 mmol) and caesium carbonate (7.50 g, 23.0 mmol) in dry acetone (200 ml) was added dropwise 1-bromo-3-(methylbromo)benzene (4.80 g, 19.2 mmol) in dry acetone (20 ml). The mixture was stirred and refluxed for 12 h and cooled to room temperature. The solvent was removed under reduced pressure. The residue was neutralized with 10% hydrochloric acid and extracted with dichloromethane. The organic layer was washed three times with water and dried over anhydrous magnesium sulfate. After removal of the solvent under reduced pressure, the residue was recrystallized from dichloromethane-hexane to give the title compound in 27% yield as a white solid. Single crystals suitable for X-ray diffraction were obtained by evaporation of a dichloromethane solution.